Surgical evacuation of an isolated interhemispheric subdural hematoma presenting with falx syndrome in the subacute period: A case report

Background: Traumatic isolated interhemispheric subdural hematoma (IHSDH) is rare, and falx syndrome is an uncommon but distinctive manifestation. Although many cases improve with conservative management, the optimal timing of surgery remains controversial. Case Description: An 89-year-old man receiving edoxaban developed progressive left lower-extremity weakness 2 days after a minor head injury. Computed tomography (CT) showed a right isolated IHSDH measuring 14 mm in maximal thickness. Neurological examination revealed left lower-extremity monoparesis with persistent foot drop. Deep tendon reflexes were symmetric, and Babinski responses were absent bilaterally. The patient reported no pain or numbness in the lower extremities, no low back pain, and no sensory symptoms in the L5 distribution. After discontinuation of edoxaban, conservative treatment was initiated. Although proximal lower-extremity strength partially improved, foot drop persisted. Follow-up CT and magnetic resonance imaging (MRI) on day 13 demonstrated a cast-like hematoma with minimal resorption and features of organization. Lumbar MRI showed no structural lesion compressing the left L5 nerve root, and evoked electromyography of the peroneal nerve was normal. Surgical evacuation was performed on day 16. Foot drop improved rapidly and recovered to Medical Research Council grade 5 by postoperative day 5. The patient regained independent ambulation after approximately 1 month of inpatient rehabilitation and was discharged with a modified Rankin Scale score of 1. Conclusion: In isolated IHSDH with falx syndrome, persistent focal motor deficit despite partial improvement may prompt reconsideration of continued observation. In this case, radiological evolution suggesting hematoma organization was considered alongside the persistent deficit when subacute evacuation was selected.